Position and/or motion encoders provide a means for determining the position and/or motion of moveable components. While a wide variety of position encoder systems have been developed and are being used, most position encoder systems can be placed into one of two categories: linear and rotary. As their respective names imply, linear encoder systems may be used to provide an indication of linear or straight-line motion whereas rotary encoders may be used to provide an indication of rotary motion.
Encoder systems of the type described above may be further characterized as analog encoder systems or digital encoder systems. Analog encoder systems provide an analog output signal, such as a voltage or current that is related to the motion detected by the encoder. Analog encoder systems typically utilize a variable resistor or resistance element that is operatively associated with the moveable element. The variable resistor converts the motion of the moveable component into the analog signal.
Digital encoder systems provide a digital output signal that is related to the motion detected by the encoder. Most digital encoder systems are optical in nature, although non-optical digital encoders are also known. An optical digital encoder typically utilizes a light source, a detector, and a code wheel or code strip. The code wheel or code strip is provided with markings or indicia thereon. The detector detects the indicia provided on the code wheel or code strip and produces a digital output signal that is related to the position or movement of the code strip with respect to the detector.
Digital encoders may provide a relative or absolute indication of the relative position of the code wheel or code strip. Generally speaking, relative encoders provide a single set of markings or indicia on the code strip. Because the single set of markings is not unique to the particular position of the code strip, relative encoder systems must utilize a homing routine on start-up in order to derive the actual position of the moveable component. Absolute position encoders typically rely on several sets of indicia on the code strip. The indicia are such that a unique signal is associated with each position of the code strip. Thus, such absolute position encoders can provide an indication of the absolute position of the moveable element without the need to first perform a homing routine.